A US National Academy of Medicine committee said Wednesday the FDA should approve clinical trials for three-parent fertilization in human embryos—with some caveats, Nature reports. In its report, the committee recommended such trials be limited to women at risk of passing along "serious mitochondrial disease" to their kids, and it wants the mitochondrial replacement techniques, or MRT, limited to male embryos only initially. That's because mitochondria is inherited from the mother, and such a restriction would confine the modified mitochondria to one generation. "We concluded that the most germane issues could be avoided if the use of these techniques were restricted by certain conditions, rather than prohibiting them altogether," committee chair Jeffrey Kahn says in a press release.
How the process would work: We have two types of DNA—nuclear DNA, which passes on genetic traits, and mitochondrial DNA. During MRT, a woman with mitochondrial DNA disease would have her nuclear DNA transferred to the nuclear DNA-free eggs of a woman whose mitochondrial DNA is just fine. This would result in three parents, with nuclear DNA from one man and one woman and mitochondrial DNA from another woman. But despite the committee's recommendation, there's still one major hitch: The federal 2016 spending bill currently in effect prohibits the FDA from greenlighting the implantation of modified embryos into women. "The future seems very hazy compared to a few months ago," a reproductive-biology specialist who's been pushing for such trials tells Nature.